Calculating Gestational Age

Step 1 - Calculating Gestational Age

In the U.S., healthcare professionals typically calculate the length of a pregnancy by gestational age . Gestational age is the number of weeks that have passed since a woman's last normal menstrual period.

Especially in the early stages of pregnancy, a physician can confirm the gestational age of your pregnancy through a physical exam.

What is Conceptional Age?

Under South Carolina's abortion law, the first trimester is defined by conceptional age.

Gestational age is not the same thing as conceptional age . Conceptional age is how much time has passed since actual conception (fertilization). Conception cannot take place until you ovulate, and that typically happens about 14 days after the start of your monthly period.

Conceptional age will always be about 14 days younger than gestational age. The average length of a full-term pregnancy is about 280 days, or 40 gestational weeks from the first day of the last period. The average length of a full-term pregnancy from the time of conception is about 266 days or 38 conceptional weeks from the day of conception.

How to Calculate Gestational Age

  1. Find the date of the first day of your last menstrual period on a calendar.
  2. Count the number of full weeks that have passed from the date in Step #1 to today's date.  For example, if your last menstrual period started on July 1st and today's date is August 1st, the gestational age is 4 weeks.

You can also use the calculator below to figure out gestational age and due date.

Pregnancy Due Date Calculator
  1. : (Required)
    (First day of bleeding.)
  2. : (Optional)
    (From first day of your period to the first day of your next period.)
    (Ranges from: 22 to 44. Default = 28.)
    (Leave 28 if unsure.)
Results
  1. From Estimated Conception Date: Estimated Gestational Age (how far along your pregnancy is): Estimated Due Date (only 5% born on their due date!): available here .

    If you do decide to receive an ultrasound and to seek an abortion, be aware that there is a required 1 hour wait time between getting an ultrasound and terminating a pregnancy (except when medically necessary).


    1 Section 44-41-10 of the South Carolina Code of Laws defines 'conception" as "the fecundation of the ovum by the spermatozoa."

    Next: The Role of Genetics

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